Coaxial transmission line



Feb. 10, 1948. K. A. YOUNG COAXIAL TRANSMISSION LINE Filed Jul 5, 1944 II a! I I mill/III ['11 j WAVE RA 770 Arne/fink. [cw/VET Ii yam a.

Patented Feb. 10, 1948 COAXIAL TRANSMISSION LINE Kenneth A. Young, Waban, Mass, assignor to Raytheon Manufacturing Company, Newton, Mass., a corporation of Delaware Application July 5, 1944, Serial No. 543,582

4 Claims.

This invention relates to coaxial transmission lines, and more particularly to an improved means for supporting the central conductor of such lines in propen alignment with the surrounding outer conductor.

It is among the objects of this invention to provide a supporting structure for the center conductor of a coaxial line which will provide greater mechanical rigidity than structures heretofore proposed and which will also possess superior electrical characteristics.

It has heretofore been proposed as disclosed in the copending application of Joseph Goldsmith, Serial Number 522,489, filed February 15, 1944, to provide a supporting connection between the outer conductor and the central conductor of a coaxial transmission line, which supporting connection is comprised entirely of metallic elements positioned within the circumference of the outer conductor.

It is among the objects of the present invention to provide an improved construction having greater mechanical rigidity, which is easier to manufacture, which will possess greater mechanical strength and rigidity, and which will permit the transmission line to transmit a much broader range of frequencies.

The above and other objects of the invention will be made apparent to those skilled in the art from a consideration of the following detailed description taken in conjunction with the accompanying drawing in which:

Fig. 1 shows a longitudinal section through a portion of a coaxial transmission line constructed in accordance with the present invention.

Fig. 2 shows a transverse section taken on line 2-2 of Fig. 1; and

Fig. 3 shows a set of curves illustrating certain operating characteristics of the invention.

Referring to the drawing, reference numeral I indicates a section of the outer tubular conductor of a coaxial transmission line having a central conductor 2. The central conductor is supported relative to the outer conductor by means of a pair of branch connectors 3 and 4 of conductive material and of substantially the same diameter as the central conductor 2. The outer ends of each of the branch connectors 3 and 4 have a curved surface conforming to the interior surface of the outer conductor I to which they are rigidly attached by means of screws 5 and 6. The joints between the curved ends of the branch connectors 3, and 4 and interior surface of the outer tubular conductor I may be made highly conductive and the rigidity of the structure improved by soldering or otherwise integrally connecting the branch connectors to the interior surface of the outer conductor after the parts have been secured in position by screws 5 and 6. The branch conneetors 3 and 4 are preferably formed integrally with sleeves 1 and 8, respectively, which sleeves are shrunk or otherwise rigidly fixed upon the conductor 2. The branch connectors 3 and 4 are so spaced upon the central conductor 2 that the distance between the center lines thereof is approximately equal to where x is the length of the waves on the transmission line. The length of the sleeves I and 8 is approximately 2 In operation since the connectors 3 and 4 are spaced at a distance of the reflections from these connectors will be out of phase by an amount corresponding to a phase difference of 180 and, therefore, the reflections will approximately cancel at frequencies corresponding to x. I

The sleeves I and 8 provide half wave length transformers extending along the inner conductor 2 for a distance of approximately or any odd multiple of one-quarter wave length, then the reflections from the branch connectors 3 and 4 will cancel at frequencies corresponding closely to A. Such a construction would be rather selective and frequencies somewhat greater or less trical spacing between the branch connectors 3 and 4. In other words if A be increased to M and the linear distance between the center lines of the connectors 3 and :3 remains the same, then this distance in terms of A1 would be less than Accordingly, if this spacing is critical at then the system is necessarily highly selective since any slight variation in A would correspond to a change in the spacing of the connectors. By the provision of the sleeves l and 8, the spacing between the connectors 3 and 4 is less critical at Accordingly, the range of frequencies which the structure will pass is greatly increased, corresponding to a, variation of around per cent of a given wave length A when the connectors 3 and 4 are spaced at approximately The length of the transformers l and 8 is likewise not highly critical at so that the frequencies passed by the structure are not restricted to a narrow band on this account. In the determination of the diameter of the transformers i and 8 it Will be simpler in most instances for those skilled in the art to determine these by direct electrical measurement of reflections in any particular frequency range rather than to determine them by analysis. The transformer diameter is not highly critical but may vary within a few hundredths of an inch for any given wave band. In the set of curves shown in Fig. 3, the ordinates represent the standing Wave ratio in power (herein denoted by 1 resulting from reflections and the abscissas represent the wave length in centimeters. The curve a shows the values of r for values of x between 9.4 and 10.4 cm. where r is the standing wave ratioin voltage due to reflections,and r is the standing wave ratio in power. As an example of a commercially successful embodiment of the invention in a line operating at. frequencies corresponding to a wave length centered at 9.8 cm. the following dimensions were used. Theinternal. diameter of conductor I was. 1.527 inches; the diameter of. the central, conductor was of an inch; the outer diameter of the transformers 1 and 8 was 0.835 inch and the length was 1.950 inches. Small variations in the diameter of the transformers were not important as may be seen from Fig. 3 in which the curve a represents the characteristics of the system when the transformer diameter is 0.825 inch and the curve b represents the characteristics when the transformer diameter is 0.835 inch. In both of the instances represented by the curves at and b, the connectors. 3 and 5. were. spaced atv a distance of 7.5 cm.. andyangularly' displaced at 90. Some of the advantages of the invention are obtained when the connectors 3 and 4 are not angularly displaced or are displaced at angles other than Curve 0 represents the characteristics of the system when, with other factors the same as in curve I), the angular displacement of the connectors 3 and i was In this case the frequency sensitivity was increased although the system still permitted tran:m-ission over a frequency band sufficiently wide for some purposes. It is therefore preferred to position the connectors 3 and 4 at an angle of about 90 since this construction permits the passage of a wider wave band. Also the construction provides a more rigid support for the central conductor than where the connectors are positioned in line or displaced at. an angle of 180. In practice as many pairs of supports 3 and 4 may be disposed along a length of a coaxial line as are necessary to support the central conductor in rigid alignment with the outer tubular conductor. Each pair of supports gives great rigidity to a, substantial length of transmission line, each pair being electrically balanced to cancel the electrical discontinuity to the connectors 3 and 4.

It will be obvious that many departures may be made from the specific details shown. For example, the transformers l and 8 may be made integrally with the conductor 2 rather than separately therefrom and the branch connectors 3 and t may be made integrally with portions 1 and 8 or may be made separately therefrom and rigidly secured thereto in any suitable manner.

While there is herein shown a particular em-- bodiment of the invention other embodiments and modifications within the scope of the appended claims will be apparent .to those skilled in the art from a consideration of the structure shown and the teachings hereof.

What is claimed is:

1. An electric transmission line for transmitting high frequency electric waves including a tubular conductor, a central conductor coaxial withsaid tubular conductor, means for maintaining said conductors in fixed spaced relation comprising a first metallic connector between said conductors, a second metallic connector spaced from said first connector by a distanceapproximately equal to three-fourths of the length of the waves on said line. and positioned at right angles thereto, said central conductor having enlargements providing transformers adjacent each of said. connectors, said. enlargements extending on each sideof the center lines of said connectors for a distance approximately equal to one-quarter of the length of the waves on said line.

2. An electric transmission line1for transmitting high frequency electric waves including a tubular conductor, a central: conductor coaxial with said tubular conductor, and' means-for maintaining said conductors in fixed spaced relation surrounding said central conductor and rigidly fixed thereto and a portion projecting from said sleeve portion and extending to and rigidly connected with said outer conductor, said T-shaped connectors being so spaced that the distance between the center lines of said projecting portions is approximately equal to three-fourths of the length of the Waves on said'line.

4. An electric transmission line for transmitting high frequency electric waves including a tubular conductor, a central conductor coaxial with said tubular conductor, means for maintaining said conductors in fixed spaced relation comprising a pair of T-shaped connectors of conductive material each including a sleeve portion surrounding said central conductor and rigidly fixed thereto and a portion projecting from said sleeve portion and extending to and rigidly connected with said outer conductor, said T-shaped connectors being so spaced that the distance be- REFERENCES CITED The following references are of record in the flle of this patent:

UNITED STATES PATENTS Number Name Date 2,284,529 Mason May 26, 1942 2,165,961 Cork et a1 July 11, 1939 2,270,416 Cork et al. Jan. 29, 1942 2,197,027 Witt Apr. 16, 1940 2,248,751 Frankel July 8, 1941 

